为什么使用原型的此javascript代码有效？
[英]Why does this javascript code using prototype work?
问题描述
I have this javascript code below: 
我下面有这个JavaScript代码：
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title></title>
<script>
function Person(first, last) {
this.first = first;
this.last = last;
}
Person.prototype.toString = function() {
return this.first + this.last;
}
var person = new Person("John", "Dough");
alert(person); // same result since alert calls toString()
</script>
</head>
<body>
</body>
</html>
The question is why does the alert(person) display "JohnDough"? 问题是为什么alert(person)显示“ JohnDough”？ To me, alert(person) should not display anything. 对我而言， alert(person)不应该显示任何内容。
2 个解决方案
解决方案1
5 已采纳 2013-01-15 15:06:39
When using alert , the method implicitly attempts to call a toString on the object. 使用alert ，该方法隐式尝试在对象上调用toString 。 In your case, toString is defined and does what you expect when explicitly calling toString . 在您的情况下，定义了toString并执行显式调用toString时的预期操作。 If you hadn't defined toString , alert would have used the native toString method of an Object and returned "[object Object]", as pointed out by @FelixKling. 如果尚未定义toString ，则alert将使用Object的本机toString方法并返回@FelixKling指出的“ [object Object]”。
解决方案2
1 2013-01-15 15:07:02
It's because that object has a toString() method. 这是因为该对象具有toString（）方法。 alert() requires a string, and will use this method for an object if it exists, or its own built-in one if not. alert（）需要一个字符串，如果存在则将对对象使用此方法，否则将对它自己的内置对象使用此方法。 As the method here returns the forename and surname, that's what you get in the alert() dialogue. 当这里的方法返回名字和姓氏时，这就是您在alert（）对话框中看到的内容。
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